This invention relates to an environmentally friendly polymerization process for making poly(phenylene ether) resin (referred to hereafter as "PPE") which comprises recycling the metal catalyst used in the oxidative polymerization of phenols.
PPE are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. Furthermore, the combination of PPE with other resins provides blends which result in additional overall properties such as chemical resistance, high strength and high flow.
The processes most generally used to produce PPE involve the self-condensation of at least one monovalent phenol in the presence of an oxygen containing gas and a catalyst comprising a metal amine complex. Manganese, copper and cobalt can be used as the metal in the catalyst and copper (I) species are the most commonly utilized. These processes are typically carried out in the presence of an organic solvent and the reaction is usually terminated by removal of the catalyst from the reaction mixture. Various chelating agents are used for this purpose with the most effective being those which bind tightly to the metal to make a soluble metal complex. The catalyst metal, as a soluble metal complex, can be efficiently removed from the polymer solution with standard extraction techniques, such as liquid-liquid extraction. The polymer can be isolated in a variety, of methods, such as anti-solvent precipitation or total isolation to provide a substantially catalyst free PPE. The metal complex in the solution also typically contains some amount of water in addition to organic solvent present as a contaminant. After the separation of the polymer from the solution, the metal complex, for example, copper complex containing solution is treated with an aqueous solution of sodium hydrosulfide to precipitate the copper as copper sulfides. The copper sulfides containing solution is disposed of as chemical waste following the appropriate governmental guidelines and laws.
It is therefore apparent that a long felt need exists for the development of methods to recycle the copper metal of the catalyst to provide an environmentally friendly PPE polymerization process.